1. Field of Invention
The invention relates to the field of transportation, and more specifically to a cross-drive transmission particularly applicable for use in differential speed-steered vehicles, particularly track-laying vehicles.
2. Description of Related Art
The use of mechanical cross-drive transmissions employing mechanical, electrical or hydraulic steering devices in tracked and other differential speed-steered vehicles has been known since approximately World War I and World War II. There is currently a growing interest in the art in using cross-drive technology in combination with exclusively electric motors to provide both drive power and steer power, the electric motors being powered by on-board engine-generator set and/or on-board stored electrical energy. Indeed certain arrangements of electro-mechanical cross-drives have been attempted in the art, with certain deficiencies.
Among these deficiencies, the cross-drive transmission architecture is conceived as an arrangement of hardware. Little if any consideration is given to potential for performance improvement, increased reliability, or reduction in lifetime cost of ownership when the drive train is designed to include power electronics, controller(s), and software function. Further, little if any consideration is given to fault tolerance in the transmission architecture.
Traditionally, the axis of rotation of the steer motor is transverse to other major axes in the transmission. The transverse steer axis adds weight and volume as compared to transmission arrangements having parallel axes. Moreover, the transverse steer axis requires the use of opposed meshes of bevel gears. Bevel gear meshes are difficult to align, expensive to manufacture and maintain, and prone to premature wear.
In certain proposed electro-mechanical arrangements, brushless DC motors are used without regard to the potential for short-circuited stator winding failure due to malfunction or due to battle damage. The permanent magnets of brushless DC motors are prone to demagnetization at elevated temperatures. Further, permanent magnet DC brushless motors have significant speed limitations arising from the back EMF inherent with fixed magnetic flux. The only solution is to provide additional windings to oppose the fixed magnetic flux of the permanent magnets at high speed, which adds weight, complexity and opportunity for failure. Finally, multiple independent winding are employed almost without regard to the implications of residual flux coupling that prevent true independent operation.
For at least these reasons, there is a need in the art for an improved electro-mechanical cross-drive transmission arrangement for differential speed-steered vehicles.